VGA arbitration: API proposal

[Alan Cox]

On Sad, 2005-03-05 at 16:37, Jon Smirl wrote:
> What about legacy code that doesn't contain vga_get/vga_put. brackets?
> You can't just do this on VT switch in the simultaneous user case.

I don't think that bit is actually the problem.

Right now the console is kernel side so is easy and can do vga_get/put
itself happily enough. The fun starts with the user space applications.
Now all of these tell the kernel they are using the graphics directly
via a vt ioctl that currently means "don't print panic messages, do
funky vt switch". That ioctl can be made to mean "older user space
application hogging the vga".

The bigger question is what the API for userspace looks like for new
"well behaved" applications that touch on VGA because the moment a user
app can lock vga we are in deadlock paradise. We may in fact need a
kernel API on the vga device to "issue vga sequence to device" which
does the locking entirely in kernel.